Free, partial, and fully constrained recovery analysis of cold-programmed shape memory epoxy/carbon nanotube nanocomposites: Experiments and predictions

Abstract

Thermally activated shape memory polymers are typically programmed by initially heating the material above the glass transition temperature (Tg), deforming to the desired shape, cooling below Tg, and unloading to fix the temporary shape. This process of deforming at high temperatures becomes a time-, labor-, and energy-expensive process while applying to large structures. Alternatively, materials with reversible plasticity shape memory property can be programmed at temperatures well below the glass transition temperature which offers several advantages over conventional programming. Here, the free, partial, and fully constrained recovery analysis of cold-programmed multi-walled carbon nanotube–reinforced epoxy nanocomposites is presented. The free recovery analysis involves heating the temporary shape above Tg without any constraints (zero stress), and for fully constrained recovery analysis, the temporary shape is held constant while heating. The partially constrained recovery behavior is studied by applying a constant stress of 10%, 25%, and 50% of the maximum recovery stress obtained from the completely constrained recovery analysis. The samples are also characterized for their thermal, morphological, and mechanical properties. A non-contact optical strain measurement method is used to measure the strains during cold-programming and shape recovery. The different recovery behaviors are analyzed by using a thermo-viscoelastic–viscoplastic model, and the predictions are compared with the experimental results.

Preparation of modified multi‐walled carbon nanotubes as a reinforcement for epoxy shape‐memory polymer composites

“…This is because the outer wall of the MWCNTs contain a small number of various functional groups, which can form hydrogen bonds with the hydroxyl groups in the epoxy resins. However, this kind of connection is much weaker than chemical bonds, so unmodified MWCNTs only slightly improve the toughness of the structure 31,32 …”

“…kind of connection is much weaker than chemical bonds, so unmodified MWCNTs only slightly improve the toughness of the structure. 31,32 The fracture surface of PM-COOH ( Figure 6E,F)…”

A Review on Additive Manufacturing of Shape-Memory Materials for Biomedical Applications

“…The programming steps include cold compression at temperature below T g , stress relaxation while keeping the strain constant at that temperature, unloading, and then the structural relaxation or resting step. [34][35][36] Note that the unloading step is accompanied by springback. Also, in cold-programmed SMPs, there will be an immediate recovery of elastic deformation, hence 100% shape fixity cannot be obtained.…”

Smart polymer nanocomposites: A review

“…The RPSM can be used for large components, and often possesses a higher recovery ratio, faster recovery rate, and improved recovery stress. Abishera et al [117] investigated the recovery performance of coldprogrammed shape memory epoxy/CNT nanocomposites for free, partial, and completely constrained conditions. The epoxy/CNT nanocomposites achieved 100% shape recovery under free recovery conditions.…”